Epidemiological and clinical studies have demonstrated that omega-3 polyunsaturated fatty acids (PUFAs) rich in fish oil may ameliorate inflammatory diseases and prevent carcinogenesis. The primary effector molecules are thought to be docosahexaenoic acid (DHA, 22:6, omega-3) and eicosapentaenoic acid (EPA, 20:5, omega-3). However, the precise mechanisms by which DHA and EPA influence hepatic carcinogenesis have not been elucidated. Therefore, the overall goal of this proposal is to understand, at a mechanistic level, how omega-3 PUFAs modulate hepatic carcinogenesis. Our overall hypothesis is that dietary supplement of omega-3 PUFAs, either alone or in combination with other standard therapy, represents an effective nontoxic approach that blocks the cyclooxygenase-2 (COX-2)-derived prostaglandin E2 (PGE2) and Wnt/beta-catenin signaling pathways and prevents hepatic carcinogenesis. This application proposes three specific aims to examine the above hypotheses. Aim 1 will examine our hypothesis that omega-3 PUFAs inhibit COX-2 and beta-catenin signaling system and prevent hepatocarcinogenesis by using chemical-induced liver tumor development in Fat-1 transgenic mice or mice with dietary supplement of DHA and EPA. Aim 2 will evaluate the effect of omega-3 PUFAs on the candidate hepatic cancer stem cells, termed oval cells. Aim 3 will utilize complementary approaches of cultured hepatocellular cancer cells, tumor xenograft models, as well as mice models of hepatic tumor induction to examine the combinational effect of omega-3 PUFAs plus blocking COX-2 or beta-catenin. Results from the proposed studies will provide important mechanistic insight and therapeutic implications for utilizing omega-3 PUFAs for the chemoprevention and treatment of human hepatocellular carcinoma.